Seismologists categorize northwest earthquakes into three different source zones. The three source zones capable of causing major destruction are the Cascadia Subduction, Deep Intraplate, and Crustal Faulting zones. The Thurston County region is vulnerable to earthquakes from all three zones.
The impacts from earthquakes to communities is well evidenced by the historic 2001 Nisqually earthquake, along with other more recent catastrophic earthquakes around the world including the 2011 Great Tohoku Earthquake in Japan and the 2021 Nippes, Haiti earthquake. Failed buildings, bridges, and other structures can trap or bury people causing injury and mass casualties. Damage to infrastructure such as roads, bridges, rail lines, runways, and almost all types of utilities is certain. Infrastructural failures can result in loss of public and private sector services and business. Communities are likely to face communication, electricity, motor fuel, natural gas, water, food, and general merchandise supply disruptions. Structural fires are a common secondary hazard from earthquake destruction. Individuals and households may be displaced due to damaged homes. A subsequent economic downturn would likely result from major transportation disruptions and loss of revenue from suspended business and services.
Cascade Earthquake Sources
Deep intraplate earthquakes occur along faults in the subducting portions of the Juan de Fuca plate, originating beneath the North American plate. Earthquakes from this zone are common in the greater Puget Sound Basin. They emanate from depths of 30 to 50 miles and can reach a strength as high as magnitude 7.5. Because of their depth, the seismic energy of deep intraplate earthquakes is distributed over a large area. The 2001 Nisqually earthquake is a historical example of an earthquake originating from this zone.
Crustal faulting earthquakes occur along faults close to the surface of the North American plate. They are produced in the upper 18 miles of the Earth’s crust, though most occur much closer to the surface. Earthquakes of this nature tend to affect a smaller area but can be more damaging relative to deep earthquakes because of their proximity to the surface.
Subduction zone earthquakes occur deep offshore when two or more tectonic plates shift into and over each other, slowing building up frictional energy until it is released. The Cascadia Subduction Zone earthquake is one example of this kind of event. Three tectonic plates (the Pacific Plate, Juan de Fuca Plate and North American Plate) converge along nearly 1,000 kilometers from northern California to Vancouver Island, British Colombia. The younger Juan de Fuca Plate is slowly spreading away from the Pacific Plate and into and under the North American Plate, building up energy. When the fault’s frictional strength is exceeded and the plates slip past each other, a megathrust will occur, resulting in “the big one,” an earthquake experts estimate will be between a magnitude 8.0 and 9.2.
Pacific Northwest Seismic Network
The Pacific Northwest Seismic Network (PNSN) is a regional network of seismographs and other instruments that are used to monitor and study earthquakes in the Pacific Northwest. The PNSN is operated by the University of Washington and the USGS, and is part of the USGS’s National Seismic System.
In addition to monitoring earthquakes, the PNSN also provides educational resources and information about earthquake preparedness to the public. You can visit the PNSN website for real-time data on earthquakes in the Pacific Northwest, as well as maps, educational resources, and information about earthquake preparedness.
United States Geological Survey
The United States Geological Survey (USGS) is a federal agency that is responsible for monitoring and studying earthquakes and other natural hazards. The USGS manages the National Seismic System to detect and measure earthquakes, and is responsible for issuing earthquake alerts and warnings to the public.
The USGS also maintains a website that provides detailed information about earthquakes, including real-time data on earthquakes around the world, maps of active fault lines, and educational resources about earthquake preparedness. Visit the USGS website to learn more about earthquake hazards.